Cnidarians - invertebrates with stinging cells

Corals

Few zones added as much to the game (in terms of aesthetics and new game play experience) as Vashj'ir in Cataclysm. Not only was it beautiful and loaded with new plants and animals, it was a completely different environment then any of the previous zones. The only way to do it again would be to have an all Air zone, where you fly all the time.

Corals are actually animals that live on a hard calcium carbonate (limestone) skeletons. They pair with a photosynthetic algae called zooxanthellae that live in the coral. The Corals live in massive polyp colonies that make up the coral heads. They grow exceptionally slowly, about 1cm a year so it takes a long time to grow into the massive coral reefs we see lining shorelines. There are thousands of species of coral in all colors and shapes and sizes. They all grow in warm, relatively shallow water.

A Crinoid attached to a coral reef - Raven_Denmark - flickrcc

Sea Anemone - AlKok - flickrcc

Anemones

You can't interact with them, so it is more flavor and color in the game. It would be interesting to have them as something that would stun and begin taking life if you got too close to the tentacles. And they have some of the predators attacking and killing prey in other zones, they could do that with these and the small colorful fish that swim around. Or there could be a quest where you have to ambush someone or something from inside a Sea Anemone but first you have to swim through it a few times to attune to the stinging tentacles so it doesn't kill you while you wait - like how a clownfish gets used to living in an anemone.

with friends like these...

They are Cnidarians stuck in the polyp phase, they lack the limestone skeleton of corals, but do not have the mobility of jellyfish. Anemones can move, just very, very slowly.

Sea Anemone 047 - kimberlinhoto - flickrcc

Sea Anemones - Screenfodder - flickrcc

Jellyfish

Jellyfish are the most mobile of the Cnidarians and they lack the limestone base of corals. They have a bell that pulsates for movement and stinging cells that capture prey. They are found in every ocean, and a few live in freshwater. Jellyfish have been around for over half a billion years and some species can grow to several meters long.

I think they could be hunter pets. It would be cool to just have one hanging out, floating around, their tentacles occasionally catching the small level-1 critters that run around.